Abstract in English:Abstract The contribution of CFRP wraps, as an anchorage system, to enhancing bond behavior between CFRP sheet and cracked concrete, was investigated. Thirty six concrete blocks (150 x 150 x 200 mm) were cast with 3ϕ12 mm steel bars embedded laterally at different spacing along the 200-mm-dimension. Half of the moist-cured blocks were subjected to a cyclic treatment in 3% chloride solution until reinforced sides cracked at an average global crack size 0.54 mm; the remaining ones were immersed in a lime solution for a similar period, as controls. Finally, the blocks were attached at their reinforced surface to CFRP sheets at different bond widths and lengths with CFRP wrap anchorages applied over portions where high shearing stresses persist during pull-off testing. The results indicate that the physical status of concrete, the geometry of main CFRP sheets, and the extension of CFRP wrap anchorage are major factors that shape the benefit from the proposed anchorage technique. Empirical models, developed to predict bond strength and slippage at ultimate stress, show very good predictability of literature data.
Abstract in English:Abstract The Structure-Soil-Structure Interaction (SSSI) phenomenon between the neighbouring structures has been interested lesser than Soil-Structure Interaction. However, in urban environments, the structures have to be constructed in the neighbourhood, and it is inevitable that these structures affect each other’s responses. This study examines the Structure-Soil-Structure Interaction effects on the response of the neighbouring frame structures. In this context, firstly the effects of the consideration of the underlying soil on the response of the structures (3-, 6-and 12-storey) are compared with the fixed base conditions. Subsequently, the variation in the acceleration and basement storey drift ratios of the structures are examined to determine the effects of the presence of the neighbouring different structures. The clear distances between the structures, structure storey numbers, soil stiffness, seismic motion and layout of the structures are the parameters taken into account. Finite element method is utilised to analyse the soil and the structures subjected to seismic excitation with direct method. It is concluded that the consideration of the neighbouring structures could positively or negatively change the responses of the structures based on the dynamic characteristics of the case.
Abstract in English:Abstract In this paper soil-structure interaction (SSI) effects are investigated while an array of Pressurized Tuned Liquid Column Dampers (PTLCD) is employed for seismic vibration control of buildings. This device represents the most general case of a passive damper, with different reduction options to other control devices obtained by simplifying the involved parameters. Soil conditions considerably affect the control device functioning, because dynamic parameters such as natural frequency, damping factor, and natural modes depend on the soil properties. A simplified mathematical model is developed for the building with multiple degrees of freedom connected to a flexible base. For the time-domain analysis, a computational routine is developed for the linearization of the equilibrium equations of the PTLCD, as well as details for the reduction to the other types of passive dampers. Several numerical examples are selected for the analysis of the damper efficiency in reducing seismic vibration considering SSI. These simulations include Kobe earthquake data, which is applied to the model to evaluate the device performance under different scenarios. It is verified the influence of SSI in the natural frequency and structural response, which is related to the earthquake frequency components. Results confirm that the array of PTLCD’s can reduce the vibration amplitudes, being more effective for soils with higher stiffness values.
Abstract in English:Abstract The need for seismic retrofitting of bridges after severe earthquakes has become important in recent years. This study examines the seismic evaluation of concrete bents of highway bridges designed and implemented according to the 1990s regulations. Compared with the older codes, 1990s codes have more complex details for connections which are evaluated by experimental and numerical methods in this research. Significant improvement was observed in the behavior of the specimens designed with 1990s codes; however, this improvement is not enough as strength degradation was also reported in the inner cycles of the hysteresis curves. Therefore, seismic improvement was performed using performance levels. Results showed that in the connection zone, the longitudinal bar slippage occurs and the performance of connection is weak. In experimental phase, a specimen was constructed with external pre-stressing in a transverse direction for retrofitting. The level of improvement in behavior was also evaluated using parameters such as energy dissipation, performance levels and force-displacement curves.
Abstract in English:Abstract In this study, a new sub-parametric strip element is developed to simulate the axially loaded composite cylindrical panel with arbitrary cutout. For this purpose, a code called SSFSM is developed in FORTRAN to analyze the buckling of panels. The first order shear deformation theory is used to form the strain-displacement relations. Spline and Lagrangian functions are used to derive element shape functions in the longitudinal and transverse directions, respectively. The computational cost of the SSFSM is decreased dramatically, as mapping functions of the strip element are very simple. The results obtained from the SSFSM are compared with those of the literature and the results obtained by ABAQUS to show the validity of the proposed approach. A parametric study is performed to show the capability of the SSFSM in calculating the panel buckling load. Results indicate that increasing the panel thickness and panel central angles cause an increase in panel buckling load. The cutout shape is an important factor influencing the panel buckling load. For instance, when the angle between the direction of big chord of the elliptical cutout and compressive load direction are 0 and 90 degrees, the panel buckling load reaches its minimum and maximum magnitude, respectively.
Abstract in English:Abstract The results of a study on the response of a side impact beam located in a car door to impact loading is presented. The side impact beam is situated in both the front and rear side doors of a vehicle between the inner and outer shells to minimise intrusion into the passenger compartment during a collision whilst absorbing as much impact energy as possible. A numerical model of a light-weight passenger car, developed by the National Crash Analysis Center (NCAC) of The George Washington University under a contract with the Federal Highway Administration (FHWA) and National Highway Traffic Safety Administration (NHTSA) of the United States Department of Transportation (US DOT), was used to simulate a side impact on the front side door using the LS-DYNA R7.1.1 explicit solver. The resulting deformation of the door from the full vehicle model was used to design an experiment for an impact test on a passenger door to validate the simulation of an equivalent numerical model. In the experiments, the car door was subjected to a drop mass of 385 kg from a height of 1.27 m so that the maximum deflection on the car door impact test would be of similar magnitude to the maximum deflection of the door in the simulation of the full car model. Drop test experiments on beams with square and round cross-sections were carried out to validate the equivalent finite element model. The side impact beam was isolated for limited geometric optimisation with a view to improving the crashworthiness of the vehicle. The optimised compound tube configuration performed better than the single tube configuration in terms of SEA (specific energy absorbed) and maximum deflection.
Abstract in English:Abstract This paper presents investigations laminated plates under moderately large transverse displacements and initial instability, through the Generalized Finite Element Methods - GFEM. The von Kármán plate hypothesis are used along with Kirchhoff and Reissner-Mindlin kinematic plate bending models to approximate transverse displacements and critical buckling loads. The generalized approximation functions are either C 0or C k continuous functions, with k being arbitrarily large. It is well known that in GFEM, when both the partition of unity (PoU) and the enrichments functions are polynomials, the stiffness matrices are singular or ill conditioned, which causes additional difficulties in applications that requires the solution of algebraic eigenvalues problems, like in the determination of natural frequencies of vibration or the initial buckling loads. Some investigations regarding this problem are presently addressed and some aspects and advantages of using C k -GFEM are observed. In addition, comparisons are presented between the classical GFEM and the Stable-GFEM (SGFEM) with regard to the evaluation of the initial critical buckling loads. The numerical experiments use reference values from analytical and numerical results obtained in the open literature.
Abstract in English:Abstract In this paper, nonlinear analysis of thick cylindrical shells with arbitrary variable thickness made of hyperelastic FGM with radially variation of material properties in nearly incompressible state under non-uniform pressure loading is presented. Thickness and pressure of the shell vary in axial direction by linear and/or nonlinear functions. The governing equilibrium equations are derived based on shear deformation theory (SDT). The Mooney-Rivlin type material is considered which is a suitable hyperelastic model for rubbers. Boundary Layer Method of the perturbation theory which is known as Matched Asymptotic Expansion (MAE) is used for solving the governing equations. A new ingenious solution and formulation have been defined during current study to simplify and abbreviate the representation of inner and outer equations components in MAE. In order to validate the results of the current analytical solution, a numerical modeling based on Finite Element Method (FEM) have been investigated. Afterwards, for different rubber case studies, the effect of material constants, inhomogeneity index, geometry and pressure profiles on displacements, stresses and hydrostatic pressure distributions resulting from MAE and FEM solution have been illustrated. This approach enables insight into the nature of the deformation and stress distribution across the wall of rubber vessels and offers the potential for investigating the mechanical functionality of blood vessels such as arteries in physiological pressure range. The results prove the effectiveness of SDT and MAE combination to derive and solve the governing equations of nonlinear problems such as nearly incompressible hyperelastic FG shells.
Abstract in English:Abstract This study aims to generalize a previously developed accurate and inexpensive 3-D zig-zag theory up to an arbitrary representation form and to determine which simplifications are yet accurate in determining transverse shear and normal stress/deformation effects on vibrations of soft-core sandwiches with not moving middle/neutral plane (pumping). Natural frequencies are calculated using displacements assumed differently across the thickness, having fixed d.o.f., not yet explored forms of representation and zig-zag functions differently accounting for the transverse normal deformability and that partially or fully fulfill physical constraints. Applications are presented for sandwich plates and beams with length-to-thickness ratios and material properties of faces and core varying within an industrial range, for which layerwise effects are very important and so suited to the evaluation of theories. Analytical solutions are found using the same trial functions and expansion order for all theories, so to evaluate their accuracy under the same conditions. The choice of the representation form and of zig-zag functions is shown immaterial if displacement field coefficients are recomputed across the thickness by enforcing the fulfillment of all physical constraints (using symbolic calculus). Furthermore, it is shown that assigning a specific role to each coefficient is immaterial, as well as exchanging the order of representation of in-plane and transverse displacement components and even that zig-zag functions could be omitted. This no longer occurs for lower-order theories with only a partial fulfillment of constraints. Pumping motions are highlighted as the first modes, which require the theories much accurately accounting for transverse normal deformability.
Abstract in English:Abstract Self-centering braces, in the current stage of development can accommodate large deformation and force levels. However, there is still a need for improvement of the energy dissipation mechanisms commonly incorporated in these braces. Yield based energy dissipation systems can overcome some of the problems faced with friction-based devices, such as susceptibility to bolt relaxation, long-term creep of friction material and excessive flexing arising in the outer tubes due to friction bolts. However, in these alternative systems multi-wave buckling of the yielding core is present, which is the leading cause of an asymmetric hysteresis of the brace. Hence, in this study, U-shape flexural plates (UFPs) are analyzed as an alternative energy-dissipating device in real scale self-centering braces with a finite element modeling approach. UFP plates yield in flexure and when comparing to direct tension/compression yielding members, they show lower strain demand, resulting in a larger displacement capacity. Implementation of the UFP units in the brace produces a flag shape hysteresis with minimal residual deformation. The proposed system provides some advantages when compared to previous models in terms of increased redundancy, symmetric hysteresis and a more gradual stiffness change.